Terahertz field driven giant nonlinear phonon response in ferroelectric semiconductor In-doped (Sn,Pb)Te

Recent advances in high-field terahertz technologies can unveil the nonlinear response of elementary excitations. This work finds large-amplitude coherent phonon dynamics in the fully anharmonic regime by intense terahertz excitation of the ferroelectric semiconductor In-doped (Sn,Pb)Te. The high-field resonant drive of soft phonons induces the dramatic shift of transient phonon frequency near the ferroelectric transition point. This highly nonlinear terahertz response quantitatively reveals a phonon potential dominated by strong anharmonicity and temporal lattice dynamics with giant atomic displacement.